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#### 2.6.2 Dual-Purpose Executable Scripts and Octave Functions

To write m-files that can act as executable programs when called from the shell or as normal functions when called from within Octave, use default input arguments initialized with the `argv` function.

If a function is called from the shell Octave will not pass any input parameters to the function and therefore the default argument is used. But when a function is called from the interpreter any arguments are passed to the function and these override the default.

Additionally, the file must end with the extension `.m` so that the interpreter will recognize it as an Octave function. Finally, the output from `argv` is a cell array of strings. It may be necessary to convert this to a numeric value with `str2double` or `str2num` before processing.

As a complete example, consider the following code located in the file `mysin.m`.

    #! /bin/octave -qf
    function retval = mysin (x = str2double (argv(){end}))
      retval = sin (x)
    endfunction

This can be called from the shell with

    mysin.m 1.5

or from Octave with

    mysin (1.5)